The long term objective of this work is to better understand differentiation in Streptomyces coelicolor through analysis of mutants, regulated genes and their interdependence. Streptomyces are gram- positive bacteria which grow as mycelium and, upon nutrient depletion, differentiate and grow upward as aerial mycelium; concurrently, secondary metabolites are produced, including many of the currently known antibiotics. To date, there are two general classes of morphological mutants in the developmental pathway of S. coelicolor, the bld and whi mutants. Many bld mutants are suppressed when grown on sugars other than glucose, suggesting an alternate pathway for aerial mycelium formation. Developmental mutants in each of these pathways will be isolated on both rich and minimal media using transposon mutagenesis. Additionally, a promoter-probe transposon, creating fusions to the reporter gene xylE, will be used to isolate developmentally regulated genes. The mutants will be characterized by mapping and cloning (aided by the drug resistance gene on the transposon). DNA sequencing and analysis of the transcript start site of the genes will be done to better understand the gene products and their regulation. This work will isolate genes involved in differentiation, some of which may have different mutant phenotypes than the bld and whi mutants since they will not be isolated in a morphological screen. The study of xylE expression of the regulated genes in the various developmental mutants isolated previously and in this study will define interdependence within the developmental pathway.